For very many years soap bars have been manufactured from fats by conversion of triglyceride components of fats into fatty acid salts and the formation of these `soaps` into bars.
Traditionally, the most important fats used in soap manufacture have been tallow (a palmatic/stearic fat rendered from animal carcasses) and coconut oil (a lauric fat). For the purposes of this specification the words `oil` and `fat` are considered interchangeable except where the context demands otherwise. The use of other palmitic/stearic fats such as palm oil and alternative lauric fats such as palm kernel, babassu or macauba oil is known.
In general the longer chain fatty acid soaps, particularly the less expensive C16 and C18 soaps (as obtained from tallow and palm oils) provide structure in the finished soap bars and prevent or retard disintegration of the soap bar on exposure to water.
The more expensive, shorter chain, lauric fat-derived, (i.e. lauric acid salts) and other soluble soaps (typically as obtained from coconut and palm kernel oil) contribute to the lathering properties of the overall composition.
A general problem in the formulation of bar soaps has been that of finding a balance between providing structure (generally obtained from the cheaper tallow/palm component) and maintaining lathering properties (generally obtained from the more costly coconut oil component) at a practical overall cost.
The fatty acid chain length distribution of a range of soap components is given below:
______________________________________ Chain length Tallow Palm Coconut Palm Kernal ______________________________________ 10 0.1 0.0 15.1 6.4 12 (lauric) 0.1 0.3 48.0 46.7 14 2.8 1.3 17.5 16.2 16 (palmitic) 24.9 47.0 9.0 8.6 18 (stearic) 20.4 4.5 9.0 8.6 20 1.8 0.3 0.0 0.4 18:1 (oleic) 43.6 36.1 5.7 16.1 18:2 4.7 9.9 2.6 2.9 18:3 1.4 0.2 0.0 0.0 Poly unsat 0.1 0.0 0.0 0.0 ______________________________________
From the table it can be seen that the coconut and palm kernel fats (together known as the lauric fats) are particularly rich in the C10-C14 saturated fatty acids, particularly fatty acid residues derived from lauric acid itself. For convenience these fats, containing saturated, relatively short chain fatty acids, will be referred to hereinafter as the `lauric` fats. This definition includes the coconut, palm kernel, babassu or macauba oils as mentioned above. In contrast, tallow and palm oil per se are an industrial source of non-lauric fats, especially those containing C16 and C18 fatty acid residues: both saturated and unsaturated residues being present in almost equal quantities. The C16 and C18 fatty acids, together with the longer chain fatty acid are referred to herein as `non-lauric` fats.
A standard measure of the degree of saturation of a fatty acid residue, or more usually of a blend of fats or fatty acids, is the so-called iodine value. The iodine value of a fatty acid residue is determined by the ability of the residue to bind iodine expressed in Mole %. Iodine binds to unsaturated fatty acids in proportion to the extent of the unsaturation and does not bind in the same manner to saturated fats. Consequently, saturated fats have low iodine values, mono unsaturated fats bind around 100 Mole % iodine and have iodine values (`IV`) of around 100. In contrast di-unsaturated fats bind around 200 Mole % and have iodine values approaching 200. The 63rd Edition of the CRC Handbook (CRC Press) gives the iodine value of beef tallow as 49.5, and for coconut oil gives an iodine value of 10.4.
In typical commercial formulations, soap bars contain from 90-50% fatty acid soaps obtained from tallow (i.e. non-lauric fats) and 10-50% of fatty acid soaps obtained from coconut (i.e. lauric fats). In particular, in countries where tallow is acceptable to consumers, most commercial soap formulations comprise 80% tallow and 20% coconut oil. In countries where tallow is unacceptable other non-lauric oils and fats, such as palm oil, replace tallow.
Some typical formulations are disclosed in the patents mentioned below:
GB 989007 (Procter & Gamble) discloses several formulations which comprise 24-33% coconut soap. The balance of the soaps in these formulations (around half the total soaps) are generally tallows (non lauric soaps) with I.V. around 48. Some hardened non-laurics are present at up to a level of 5%.
EP 194126 (Procter & Gamble) discloses omega-phase soap formulations with a 50/50 coco/tallow fat charge of an I.V. about 25. The fats are described as comprising `touch-hardened` tallow/coconut fatty acid blends, i.e. no substantial hydrogenation of the fats has taken place. The I.V. of tallow is normally about 50, and coconut about 10 therefore a total I.V. of 25 is not inconsistent with the use of these materials. Touch-hardening is a well known technique used to improve the keepability of oils and fats by removing oxidation sensitive components and consequently delaying the onset of rancidity.
WO 84/04929 (Henkel) discloses a soap bar comprising at least 40% lauric acid soaps. The examples disclose formulations with coconut fatty acid soaps of the `Edenor` [RTM] type.
In addition to fatty acid soaps per se, toilet bars can contain free fatty acid. The addition of free fatty acid is known as `superfatting` and superfatting at a 5-10% free fatty acid level is known to give a copious, creamy lather. Other superfatting agents include citric and other acids which function by promoting the formation of free fatty acids in the fat blend.
The conventional soap making process as applied to the manufacture of toilet soaps is well documented in the literature. In outline the process is as follows. In conventional `wet` soap making, fats, i.e. tallow and coconut oil blends, are saponified in the presence of an alkali (typically NaOH) to yield fatty acids as alkaline soaps and glycerol. The glycerol is extracted with brine to give a dilute fatty acid soap solution containing around 70% soap and 30% aqueous phase. This soap solution is dried, typically by heating in heat exchangers to circa 130.degree. C. and drying under vacuum, to a water content of around 12%, and finished by milling, plodding and stamping into bars.
One known defect in soap bars is so-called `grittiness` It is believed that grittiness is caused by overdrying of a portion of the soap during the vacuum drying stage which leads to a poor barfeel. The problem of grittiness becomes progressively more significant at lower water contents and while grittiness can be controlled at laboratory scale it is more difficult to prevent grittiness at pilot plant and factory scale.
The stamping step, is typically conducted at around 250 or more bars per minute in a conventional soap line having several bars stamped in parallel.
A problem commonly encountered in stamping of bars is so-called `die-blocking`. This occurs when a billet of soap does not release from the die after the stamping operation. The consequence of die blocking is that the process line must be stopped and the die cleared manually. This has a serious effect on throughput, as it is difficult to stop, clear and restart the stamping apparatus quickly and safely. During this down-time, the soap being produced upstream of the stamping apparatus must be diverted and recycled.
In general, superfatting of bars makes the bars softer and more difficult to process, particularly in the plodding and stamping step. For this reason, superfatted bars are processed at a low water content: typically 82% total fatty matter (TFM) as opposed to the more conventional 78% TFM. If conventional water contents are used, superfatted bars are difficult to manufacture. Preferably superfatted bars are manufactured at a low temperature to increase the hardness of the billets and to reduce adhesion of the billets to the dies (see Woollatt: `The manufacture of soaps, other detergents and glycerine`, page 267, paragraph 6.5.6). As will be appreciated, the decrease in the water content of the bars associated with superfatting increases the cost of the bars as the proportion of fatty matter in the bars is increased.
A further drawback of compositions containing fatty acid soap is harshness, a property which is determined by a number of tests as will be elaborated upon hereafter. Known solutions to the problem of harshness include reduction of the level of soap present and replacement of the balance of the composition by so-called co-actives. It has also been suggested that superfatting improves mildness but the improvement is not considered as significant as that obtained by the use of co-actives. As with superfatting agents, a recognized problem engendered by the presence of co-actives is a loss of product structure in the resulting soap bars.
WO 93/04161 (Procter & Gamble) discloses bars which comprise a mixture of soap, a C.sub.14 -C.sub.20 alkyl polyethoxylate nonionic detergent surfactant and a C.sub.10 -C.sub.18 acyl isethionate. The soap contains at least tallow and is often a mixture with palm stearin and/or coconut. Also included in the formulations are cationic polymeric skin mildness aids and, as moisturizers, free fatty acids.
In order to overcome the problem of loss of structure, soap bars which comprise co-actives have been manufactured by processes which, while being successful, increase the cost of the eventual products. Several such processes are known.
GB 2182343-A (Procter & Gamble) discloses toilet soaps comprising a fatty acid soap, a synthetic surfactant co-active and a water soluble polymer. In order to reduce the softening effect of the co-active it is necessary for some of the soap to be present in the so-called beta-crystalline phase and crystallization in this phase can only be achieved by the application of high shear (i.e. energetic working) in an additional processing step after the drying step and prior to finishing.
EP 363215 (Colgate) discloses the production of toilet soap bars from soap and an ethoxylated surfactant co-active. This soap composition needs to be dried to below a critical 5% wt moisture content in order to harden the material sufficiently for processing into bar form using conventional soap making/forming equipment. This drying step requires additional equipment in the form of batch drying trays to be used prior to soap finishing.
EP 311343 (Procter & Gamble) discloses the combined use of a beta-crystalline phase, an ethoxylated nonionic surfactant co-active and a water soluble polymer. As described above, these compositional modifications require modification of the soap processing line to provide for the energetic working needed to form the beta-crystalline phase.
GB 2243614 (Proctor & Gamble) discloses a beta-phase soap bar prepared by a process involving the use of one or more mills (see page 13 line 30ff). The bars have less than about 25% short chain soaps (see page 4 line 37ff) as the presence of these soaps interferes with the formation of the beta-phase.
It can be seen from the foregoing that each of the known, alternative processes for the production of soap bars containing co-actives require the provision of further processing apparatus, particularly in the form of drying and/or energetic working apparatus and the additional processing step which makes use of this apparatus prior to soap finishing. This increases the cost of processing and consequently increases the cost of the bars produced.
In addition to provision of structure, it is known that the beta-phase of soap provides translucency in certain formulations. It is also known that these formulations cannot contain significant quantities of superfatting agents (at or above 2% wt) as the presence of larger quantities of superfatting agent interferes with the formation of the beta phase.
From the above it can be seen that there is a need for mild bars which do not have the processing problems associated with the use of superfatting agents and co-actives, which can be made without difficulty on conventional soap production lines without substantial modification of the lines and yet provide a product with reduced harshness while maintaining lathering and structural properties. It is desirable that soap bars should not suffer from the defect of grittiness and it is also desirable that these bars have a composition which contains relatively low levels of the significantly more expensive lauric fats.